RTC 读写指令及测试程序

在 Linux 系统中，指令 date 和 hwclock 都可以读写时间

date：读写系统时间，写时间需要管理员权限

hwclock：读写硬件时间，也就是 rtc 模块的时间，读写都必须有管理员权限

// 读取当前系统时间
$ date
Thu Oct 24 03:03:13 UTC 2019
// 普通用户设置时间失败
$ date 102411032019.00
date: cannot set date: Operation not permitted
Thu Oct 24 11:03:00 UTC 2019
// 超级用户设置时间成功，格式:月日时分年.秒
$ sudo date 102411032019.00
Thu Oct 24 11:03:00 UTC 2019
// 读取当前系统时间，确认时间设置成功
// 小时与设置的11点不同，这是由于时区造成的
$ date
Thu Oct 24 03:03:38 UTC 2019

rtc 测试 demo：

#include <stdio.h>
#include <stdlib.h>
#include <linux/rtc.h>
#include <sys/ioctl.h>
#include <sys/time.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <time.h>

int main(int argc, char *argv[])
{
    int fd, retval;
    struct rtc_time rtc_tm;
    time_t timep;
    struct tm *p;

    fd = open("/dev/rtc", O_RDONLY);
    if (fd == -1) {
        fprintf(stderr, "open /dev/rtc error
");
        exit(errno);
    }

    /* Read the RTC time/date */
    retval = ioctl(fd, RTC_RD_TIME, &rtc_tm);
    if (retval == -1) {
        perror("ioctl");
        exit(errno);
    }

    fprintf(stderr, "RTC date/time: %d/%d/%d %02d:%02d:%02d
",
        rtc_tm.tm_mday, rtc_tm.tm_mon + 1, rtc_tm.tm_year + 1900,
        rtc_tm.tm_hour, rtc_tm.tm_min, rtc_tm.tm_sec);
    time(&timep);
    p = gmtime(&timep);
    fprintf(stderr, "OS date/time(UTC): %d/%d/%d %02d:%02d:%02d
",
        p->tm_mday, p->tm_mon + 1, p->tm_year + 1900,
        p->tm_hour, p->tm_min, p->tm_sec);
    p = localtime(&timep);
    fprintf(stderr, "OS date/time(Local): %d/%d/%d %02d:%02d:%02d
",
        p->tm_mday, p->tm_mon + 1, p->tm_year + 1900,
        p->tm_hour, p->tm_min, p->tm_sec);
    
    rtc_tm.tm_mday = 15;
    rtc_tm.tm_mon = 11;
    rtc_tm.tm_hour = 15;
    rtc_tm.tm_min = 15;
    retval = ioctl(fd, RTC_SET_TIME, &rtc_tm);
    if (retval == -1) {
        perror("ioctl");
        exit(errno);
    }
    
    /* Write the RTC time/date */
    retval = ioctl(fd, RTC_RD_TIME, &rtc_tm);
    if (retval == -1) {
        perror("ioctl");
        exit(errno);
    }

    fprintf(stderr, "RTC date/time: %d/%d/%d %02d:%02d:%02d
",
        rtc_tm.tm_mday, rtc_tm.tm_mon + 1, rtc_tm.tm_year + 1900,
        rtc_tm.tm_hour, rtc_tm.tm_min, rtc_tm.tm_sec);
    time(&timep);
    p = gmtime(&timep);
    fprintf(stderr, "OS date/time(UTC): %d/%d/%d %02d:%02d:%02d
",
        p->tm_mday, p->tm_mon + 1, p->tm_year + 1900,
        p->tm_hour, p->tm_min, p->tm_sec);
    p = localtime(&timep);
    fprintf(stderr, "OS date/time(Local): %d/%d/%d %02d:%02d:%02d
",
        p->tm_mday, p->tm_mon + 1, p->tm_year + 1900,
        p->tm_hour, p->tm_min, p->tm_sec);
    
    close(fd);
        
    return 0;
}